The present invention relates to a printer and more particularly, to a technique for enabling printing operation of print data with use of suitable sizes of buffer memory and full dot memory even when the amount of print data corresponding to one page becomes large.
The present invention further relates to a technique which can effectively applied to a cut-sheet printer which, when a printing cut sheet jam occurs and it is desired to again start its printing operation from the jam occurrence page, can ensure the printing from the jam occurrence page.
In a conventional printer of the type referred to above, when a paper jam (abnormal paper feed) takes place during continuous printing operation, the jam occurrence page print data and the subsequent page print data fail to be printed out. This is recovered usually by again printing these data after the jam fault has been removed.
For example, a printer disclosed in JP-A-64-47566 comprises a data memory which has a capacity of being able to store more than one page print data and thus can reprint a paper jam occurrence page on the basis of the print data stored in the data memory.
Another printer disclosed in JP-A-3-26561 is provided with a means for storing therein page positions on a data memory for storing print data in a data output order, so that when it became necessary to return the current page number due to the occurrence of a paper jam, the contents of the storage means are referred to and necessary print data is extracted from the data memory for its reprinting operation.
Further, in a paper jam recovery system of a printer disclosed in JP-A-1-202467, there are provided a bit map memory for storing bit data to be written in a drum of the printer and a backup memory for saving the bit data written in the bit map memory as associated with its page number, so that, in case of a paper jam, reprinting operation is carried out over the jam occurrence page with use of the data from the backup memory.
In this way, in order to ensure the printed result of the print data including the jam occurrence page data even when a paper jam occurs, such means and memories as mentioned above are provided.
The aforementioned prior art techniques, however, cannot recently cope with such a paper jam problem, because one page of print data requires various sorts of data such as not only letter data but also graphics data and image data and also requires a page description language. In this way, the prior art techniques cannot cope with the needs of a recent tendency of an increasingly large amount of data to be handled.
For example, when the amount of data corresponding to one page is increased, the data memory or print data memory in the printer of the JP-A-64-47566 or JP-A-3-26561 must have a much larger memory capacity.
Further, in these prior art systems, an upper data limit per page is not determined, that is, when print data exceeding the memory capacity are handled, the print data memory cannot store all the print data therein. Thus, even when a paper jam occurs, reprinting for the jam occurrence page cannot be attained and the printed result cannot be ensured.
Meanwhile, a cut sheet, double-side printer enabling high speed printing generally has a plurality of bit map memories for the double sides. For this reason, when the paper jam recovery system of the printer of JP-A-1-202467 is applied to the double-side printer, the double-side printer must have a plurality of backup memories.
Accordingly, the prior art technique has a problem that, when it is desired to handle a mixed media data of letters, graphics and image data, a variation in the amount of print data per page, in some cases, becomes as large as to reach megabyte, so that the capacity of the page buffer as its upper limit cannot be determined.
In addition, the prior art technique is also defective in that a plurality of full dot memories are necessary for printing control and the capacity of each memory is usually about 2 megabytes, so that, when a backup memory is provided for the full dot memories to save pages, the capacity of the backup memory must be several megabytes, which leads to an increased cost.